Self-attaching female fasteners, including pierce and clinch nuts, formed by cold header techniques and secondary press operations generally include a body portion having an end face, a central pilot portion projecting from the end face of the body portion having a bore through the central pilot portion, an annular groove in the end face of the body portion surrounding the pilot portion and an annular panel support face or flange portion surrounding the annular groove. Generally, at least one of the inner and outer side walls of the annular groove are inclined toward the other side wall to provide a restricted opening to the annular groove adjacent the annular panel support face to improve retention of the fastener following installation. Further improved retention of the fastener on a panel is provided by inclining both the inner and outer side walls of the annular groove toward the opposing side wall forming a “dovetail” shaped re-entrant groove. When the panel is deformed against the bottom wall of the groove by a die member or die button having a projecting annular lip configured to be received in the annular groove, the panel is simultaneously deformed beneath the undercuts provided by the dovetail shaped re-entrant groove. Alternatively, the outer side wall of the annular groove may be inclined toward the pilot portion and the pilot portion may be deformed radially outwardly during installation as disclosed, for example, in U.S. Pat. No. 6,276,040 to form a secure installation having sufficient push-off strength. However, most installations of self-attaching nuts also require sufficient torque resistance or anti-rotation means preventing rotation of the self-attaching fastener on the panel following installation, particularly where the nut and panel assembly is attached to a second component by a bolt or other male threaded member using a torque wrench or the like.
The prior art discloses various anti-rotation or torque resistant means for self-attaching female fasteners of this type. For example, U.S. Pat. No. 5,531,552, assigned to the predecessor in interest of this application, discloses forming a plurality of circumferentially spaced protrusions having radial channels therebetween in the bottom wall of the groove which provides improved torque resistance. U.S. Pat. No. 5,549,430, also assigned to the predecessor in interest of the assignee of this application, discloses a self-attaching nut of this type, wherein the bottom wall of the groove includes a plurality of spaced arcuate or semi-circular protrusions integral with the pilot portion which provide improved torque resistance, but which also deforms panel metal beneath the inclined outer side wall of the annular groove, also providing improved push-off strength following installation. U.S. Pat. No. 5,782,594 discloses a pierce nut having a central recess, rather than a groove having an inner side wall and a plurality of circumferentially spaced radial notches or pockets formed in the panel support face which, when formed by a die member, forms radially inwardly projecting bead-like projections in the side wall of the recess, providing improved torque resistance. The above-referenced U.S. Pat. No. 6,276,040, also discloses opposed V-shaped webs integral with the bottom wall of a dovetail shaped annular groove and the opposed inner and outer side walls of the annular groove. Further, the prior art includes pierce nuts of this type having rectangular radial ribs or lugs which bridge the bottom wall of the annular groove and are integral with both the inner and outer side walls of the groove. However, where the ribs are integral with both the inner and outer side walls of the annular groove, deformation of a panel against the ribs may cause deformation or distortion of the thread cylinder unless the pilot is reinforced.
However, many applications of self-attaching nuts of this type formed by cold heading require further improved integrity of the nut and panel assembly, including improved torsion resistance and push-off strength. The embodiments of the improved self-attaching nut of this invention provides improved integrity of the nut and panel assembly, including improved torsion resistance and push-off strength.